This invention relates to turbine blade cooling systems. More particularly, but not exclusively the invention relates to turbine blade cooling systems and turbine assemblies for gas turbine engines.
It is sometimes necessary to provide the intermediate pressure turbine of a gas turbine engine with a moderate cooling. Known techniques for cooling turbine blades in gas turbine engines use air from a pre-swirl system. However such systems for cooling are costly and inefficient and there are significant energy losses associated with such systems.
According to one aspect of this invention there is provided a turbine assembly comprising a rotatable support arrangement, a plurality of turbine blades extending radially outwardly from the support arrangement, and flow path means extending radially in each of the blades for a flow of cooling fluid therethrough, and the flow path means being connectable to a supply of relatively cold cooling fluid, wherein the flow path means is arranged such that the relatively cold cooling fluid is driven radially outwardly through the flow path means substantially wholly by the centrifugal force generated by rotation of the assembly in operation, to drive relatively hot cooling fluid radially inwardly through the flow path means.
Preferably, the flow path means comprises a first flow path through which said relatively cold cooling fluid can pass and a second flow path through which said relatively hot cooling fluid can pass.
According to another aspect of this invention there is provided a method of cooling a turbine assembly, the assembly comprising a rotatable support arrangement and a plurality of turbine blades extending radially outwardly from the support arrangement, and flow path means extending radially in each of the blades for a flow of cooling fluid therethrough, wherein the method comprises arranging the flow path means in fluid communication with a supply of relatively cold cooling fluid and rotating the support arrangement to drive the relatively cold cooling fluid radially outwardly through the flow path means substantially wholly by the centrifugal force generated by rotation of the assembly in operation, and allowing said cooling fluid to be heated in said blades, whereby relatively hot cooling fluid is displaced radially inwardly through the cooling path means by the flow of said relatively cold cooling fluid.
The support arrangement may define a second flow path means in fluid communication with the first mentioned flow path means. The second flow path means may comprise a feed flow path extending from an inlet to the first flow path and an exhaust flow path from the second flow path to an outlet. The inlet and outlet may be provided in substantially the same region.
The preferred embodiment of the turbine assembly is an intermediate pressure turbine assembly. In the preferred embodiment, fluid flowing along the feed flow path can pass into the first flow path in each blade to extract heat therefrom and thereafter can flow into the second flow path to pass into the exhaust flow path to be exhausted via the outlet.
Preferably, the inlet of the cooling path means is defined at a central region of the support arrangement. The outlet of the cooling path means may also be defined at the central region of the support arrangement. In one embodiment, substantially all the cooling fluid entering the first mentioned flow path means is delivered to the second flow path means. Substantially all the cooling fluid entering the feed flow path may be delivered to the first mentioned flow path means, and substantially all the cooling fluid entering the exhaust flow path may be exhausted from the outlet.
The support arrangement may comprise a support disc upon which said plurality of turbine blades can be mounted and said support arrangement may further include a cover member arranged over a face of the disc. The cover member may be adapted to hold the turbine blades on the disc.
In one embodiment, at least a part of the flow path means may extend generally radially along the support disc. A further part of the flow path means may extend generally circumferentially of the disc. In one embodiment, part of the feed flow path extends generally radially of the disc and part of the exhaust flow path extends generally radially of the disc. A further part of the feed flow path may extend generally circumferentially of the disc, and a further part of the exhaust flow path may also extend generally circumferentially of the disc.
The flow path means may be defined by the cover member. Preferably, the flow path means is defined between the cover member and the disc. In one embodiment, the feed and exhaust flow paths are provided generally in a plane, said plane being generally parallel to the plane of the disc. In another embodiment, the feed and exhaust flow paths are provided in a plane generally transverse to the plane of the disc.
Each turbine blade may have a securing portion to secure the blade to the disc, and an opening may be defined in the securing portion through which cooling fluid can enter the first flow path in the blade. Each blade may further include a shank and an aerofoil section, the shank extending between the securing portion and the aerofoil section. A shroud member may be provided between the shank and the aerofoil section, whereby, when assembled, the shroud members of adjacent turbine blades engage each other to define a space between the shroud and the disc. In one embodiment, an opening for the second flow path in the blade may be defined in the shank, whereby cooling fluid in the second flow path in each blade can be passed from the blade into the space.
The exhaust path in the support arrangement may be in fluid communication with the space, whereby cooling fluid may flow from said second path means in the blade to the exhaust path means via said space.